Airborne photographing apparatus

ABSTRACT

An apparatus for photographing the ground continuously from an airplane, and for recording the photographed images in digital form in real time. A three-line sensor camera comprising a forward-oblique line sensor, a vertical line sensor and a backward-oblique line sensor is on board. The three-line sensor camera has a gyro integrally connected thereto. Data of the camera&#39;s attitude available from the gyro, digital data of the land images available from the camera and data of the airplane&#39;s position available from an airborne GPS are recorded and reproduced. The camera is controlled with the aid of the gyro so that its optical axis may be held in a vertical direction at all times.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an airborne apparatus for photographinga selected piece of ground surface to provide data of ground image fordetermining the shape and height of the land.

2. Description of the Prior Art

Air photographs have been widely used for determining the shape andheight of a selected piece of land. In general, air photographs aretaken of overlapping area sections of a selected piece of land, therebyproviding a series of latent images taken at regular intervals on afilm. The film is developed, and the developed images are printed.

Alternatively, an airborne scanner-and-line sensor is used to providerequired land images in the form of digital data.

Each of the series of the so taken pictures, however, is made up by thecollection of image fractions recorded by beams of light reflected indifferent directions, and therefore such collection of image fractionsis not continuous. In addition to this problem the image quality varieswith the photosensitivity of the film, developing and printingconditions and other factors.

Nobody can tell what image is like before developing, and therefore, ifpictures are found to be defective or useless after developing, the samepictures have to be taken again.

To determine the shape and height of a selected piece of land from airphotographs three coordinate points X₀, Y₀ and Z₀ of the instantaneousposition of the airborne camera and three inclinations about threecoordinate axes ω, φ and u must be determined analytically by usingknown points (reference points) in the coordinate system. A lot of workis required for finding the reference points in the coordinate system.

To automatize such air photographing-and-analyzing work it is necessaryto have an analogue-to-digital conversion occur for the developed filmfor digitization.

The present invention aimes at photographing continuously a selectedpiece of land by an airborne three-line sensor camera, and at making arecord the land image data in the form of digital data directly from theso taken air photographs. Also, the present invention aimes at effectingfeedback control of the attitude of the airborne camera by usingattitude data provided by a gyro associated with the three-line sensorcamera, thereby setting the camera so that its optical axis may bevertical at all times, thus assuring that distortion-free images may beprovided. Finally, the present invention aimes at making a record ofeach of the attitude data provided by the gyro and the instantaneousposition data provided by a GPS in addition to the record of land imagedata recorded in the form of digital data, thereby permitting a requiredcorrection to be made later by using appropriate softwares.

SUMMARY OF THE INVENTION

An airborne photographing apparatus according to the present inventioncomprises: an airborne three-line sensor camera for taking pictures of aselected piece of land in three directions, that is, forward obliquely,vertically and backward obliquely; a gyro mounted in the housing of thethree-line sensor camera for determining the attitude of the camerawhile photographing; a GPS for providing the instantaneous position dataof the camera in the three-dimensional space; a stabilizer forcontrolling the attitude of the camera to set its optical axis to bevertical at all times, and at the same time for absorbing the vibrationof the aeroplane; a data processing unit for processing the attitudedata from the gyro and the position data from the GPS and outputtingsignals for controlling the stabilizer; a data recorder for recordingthe land image data from the camera, the attitude data from the gyro andthe position data from the GPS; an image display for showing the landimage data from the camera; and a data analyzer for converting the landimage data from the camera into the land image data given in terms offixed coordinates on the basis of the land image data, attitude data andposition data all recorded by the data recorder, and for outputting theso converted land image data.

The airborne three-line sensor camera is used in taking pictures of aselected piece of land.

The gyro is mounted in the housing of the three-line sensor camera, andis used in providing data of the attitude of the camera whilephotographing.

The GPS is used in determining the instantaneous position data of thecamera while photographing in the three-dimensional space.

The stabilizer functions to control the attitude of the camera to setits optical axis to be vertical at all times, and at the same time,absorb the vibration of the aeroplane.

The data processing unit is used in processing the attitude data fromthe gyro and the position data from the GPS and outputting signals forcontrolling the stabilizer.

The data recorder is used in recording the land image data from thecamera, the attitude data from the gyro and the position data from theGPS all together.

The image display is used in showing the land image data from thecamera.

The data analyzer is used in converting the land image data from thecamera into the land image data given in terms of fixed coordinates onthe basis of the land image data, attitude data and position data allrecorded by the data recorder, and for outputting the so converted landimage data.

With this arrangement the instantaneous position of the three-linesensor camera (X₀ Y₀ and Z₀) and the inclinations of the camera aboutthree coordinate axes (ω, φ and u) can be determined for each minutetime, that is, as a function of time, thus making the referencepoint-finding work unnecessary, or reducing such work to a possibleminimum. Also, the stereomatching can be performed by using a computer.These can provide technical innovations.

The conventional stereomatching determines a three dimensionalcoordinate on a selected piece of land by determining the crossing oftwo beams of light projected at different angles. In contrast, thethree-line sensor system adopted by the present invention uses threedifferent beams of light projected vertically, forward-obliquely andbackward-obliquely respectively, and therefore, it has enough redundancyto permit a required error checking, and accordingly the accuracy withwhich the shape and height of a piece of land can be determined isimproved.

BRIEF DESCRIPTION OF THE DRAWING

Other objects and advantages of the present invention may be understoodfrom the following description of a preferred embodiment which is shownin the accompanying drawings:

FIG. 1 is a block diagram of an airborne photographing apparatusaccording to one embodiment of the present invention;

FIG. 2 shows how the airborne three-line sensor camera works;

FIG. 3 shows how the GPS determines the instantaneous position of theairplane;

FIG. 4 shows the stabilizer and associated control;

FIG. 5 shows how the three-line sensor camera takes a picture of aselected piece of land when the airplane is on the proper course withits attitude retained ideally;

FIG. 6 shows how the three-line sensor camera takes a picture of aselected piece of land when the airplane is rolling;

FIG. 7 shows how the three-line sensor camera takes a picture of aselected piece of land when the airplane is pitching;

FIG. 8 shows how the three-line sensor camera takes a picture of aselected piece of land when the airplane is yawing; and

FIG. 9 is a flow chart according to which the data processing uniteffects the processing of data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the accompanying drawings, an airborne photographingapparatus according to one embodiment of the present invention isdescribed as follows. Referring particularly to FIG. 1, the apparatususes a three-line sensor camera 1, which comprises three CCD linesensors 1a, 1b and 1c arranged in parallel, each taking a picture of aselected piece of land at a different angle, and analogue-to-digitalconverting the so taken land images for sending the digital land imagedata to an associated data processing unit 5.

A gyro 2 is fixed to the housing of the three-line sensor camera 1, thusdetermining the attitude of the camera in terms of the inclinationsabout three coordinate axes (roll angle ω, pitch angle φ and yaw angleu).

A global positioning system (abbreviated as "GPS") 3 is responsive toelectromagnetic waves from selected artificial satellites fordetermining the instantaneous position of the receiving object (airplaneor ship) in the three dimensional space.

In the present invention an airborne GPS is used for determining theinstantaneous position of the three-line sensor camera 1 (X₀, Y₀, Z₀)while photographing in the three-dimensional space.

FIG. 2 illustrates how the three-line sensor system used in the presentinvention works.

As seen from FIG. 2, three different corresponding points (x_(i),y_(i),z_(i) : i=1, 2 or 3) are formed on three digital land imagesrespectively.

The instantaneous sensor position is given by (X_(0i), Y_(0i), Z_(0i)),and the different inclinations are given by (ω_(i), φ_(i) and u_(i)).

One of the corresponding points (x, y) is given by the followingequations: ##EQU1## , where f stands for focal length.

These equations can be converted as follows: ##EQU2##

a₁, - - - a₉ are given by the following rotational matrixes. ##EQU3##

d: distane from the center of the arranged sensor

The above two equations are held for each corresponding point, and thethree-dimensional coordinates (X, Y, Z) in the land surface can bedetermined from six equations in total according to the method of leastsquares.

FIG. 3 shows how the GPS works in determining the instantaneous positionof the camera.

As seen from FIG. 3, the airplane or ship A bearing a GPS receivessignals from four artificial satellites S selected among those flying inspace, determining the distance to each artificial satellite. Theinstantaneous position of each artificial satellite is determined at thetime of photographing by using the presumable orbit data of theartificial satellite S available from the stationary station P on theground, and then, the receiving station (airplane A) is located on thesurface of each sphere having a radius of the so determined distancefrom the stationary station P to the airplane A with its center on theartificial satellite. Such calculations are performed on four or moreartificial satellites, and the receiving station (airplane A) is locatedcontinuously in the kinematic or differential mode.

A stabilizer 4 (FIG. 1) absorbes the vibration of the airplane, and atthe same time it controlls the attitude of the airborne camera.

FIG. 4 shows the controlling mechanism of the stabilizer. As shown inthis drawing, the three-line sensor camera 1 has a gyro 2 integrallyconnected thereto, and the gyro 2 provides voltage signals to controlthe motors (M1, M2, M3) of the three-axis attitude control mechanism,thereby putting the camera in alignment with a given fixed direction.

FIGS. 5 to 8 show how the three-line sensor camera 1 photographs a pieceof land.

Referring to FIG. 5, the airplane A is flying on a given course at apredetermined height and in a predetermined direction. In this idealcase the airborne three-line sensor camera 1 is directed vertically allthe time, thus providing complete land images, which are free ofdistortions, and not losing any fraction of data.

It is, actually impossible, however, that the airplane will always flyon the ideal course, and it is liable to deviate from the proper coursewhen being adversly affected by wind and other weather factors. FIG. 6illustrates how the piece of land is swept when the airplane is rolling;FIG. 7 illustrates how the piece of land is swept when the airplane ispitching; and finally FIG. 8 illustrates how the piece of land is sweptwhen the airplane is yawing.

It is, therefore, necessary that the three-axis attitude controlmechanism be controlled in real time so as to hold the attitude of theairborne camera vertically at a fixed height, thus putting its sensorsin condition in which they may traverse the proper flight course.

Assume that the attitude of the airplane is recorded while photographingin place of controlling the attitude of the airplane, thus allowing theairborne camera to scan out of the land-sweeping range when the airplaneinclines to follow the correct flight course. In this case thereproduced land image will be incomplete, losing some fractions of landimage data. Even though the airplane is on the correct flight course,the airborne camera when inclining about any of the three coordinateaxes as shown in FIGS. 6 to 8, will fail to scan across the selectedstrip of land completely, and the reproduced image cannot beinterpolated or extrapolated for providing a complete land image. Suchinterpolation or extrapolation, if possible, will take much time forcomputor processing.

FIG. 9 is a flowchart showing the processing of data carried out by anassociated data processor.

As shown in FIG. 9, the data processor 5 effects the processing ofattitude data from the gyro 2 and the instantaneous position data fromthe GPS 3 for outputting signals to control the stabilizer 4.

A decision as to whether or not the airplane is flying straight on theproper flight course can be made from the instantaneous position datafrom the GPS 3. Also, a decision as to whether or not the airplaneshould turn can be made from the data of yaw angle available from thegyro 2 (particularly such turn caused by a traversing wind). Accordinglya required correction can be made for directing the airborne camera tobe transverse to the proper flight course (or making the airborne camerato scan transversly across the strip of land), which correction iscalled "drift-angle correction" or "yaw correction".

The data processor 5 transfers land image data from the camera 1, dataof the attitude of the airplane from the gyro 2, and data of theinstantaneous position of the airplane from the GPS 3 to the datarecorder 6. From the data signals are produced to control the motors ofthe stabilizer for setting the optical axis of the airborne camera 1 tobe vertical.

The data recorder 6 is a digital recorder which is capable of recordingdigital data at an increased rate, thus permitting the real-timerecording of the land image data, which is transfered from the camera 1to the data processor 5. At the same time, data of the attitudeavailable from the gyro 2, and data of the instantaneous positionavailable from the GPS 3 are recorded synchronously with each scanningline of the land image data.

The image display 7 shows the land image taken by the airborne camera 1in real time, thereby permitting a decision as to whether or not theairplane is now on the proper flight course to be made.

The data analizer 8 on the ground makes required corrections of the lensaberration, CCD characteristics and other proper factors on the basis ofland image data, the attitude data and the position data all recorded onthe data recorder 6 to provide land image data in terms of fixedcoordinates for each pixel. The land image data thus provided can beused in driving the software pertaining to the digital photogrametry.

As may be understood from the above, a three-line sensor cameraphotographs a selected piece of land continuously to provide land imagedata taken at three different angles, thereby permitting the analyzingof the land in terms of shape and height in real time. Also, attitudedata is available from the gyro integrally connected to the camera, andthe feed-back controlling of the camera is effected on the basis of theattitude data so as to direct the optical axis of the camera in thevertical direction as all times, and at the same time to direct the linesensors to transverse the flying course, thus assuring that the landimage data is free of distortion. Thanks to this art line sensors whichhave been hitherto thought to be used only in stable artificialsatellites can be on board for recording of digital land images.

In addition to land image data recorded in digital form the attitudedata available from the gyro and the position data available from theGPS are recorded together.

Advantageously all these recorded data are used for processingphotographs, thereby permitting the digital photomapping with precisionat an increased efficiency, and no reference-point finding work isunnecessary.

What is claimed is:
 1. An airborne photographing apparatus, comprising:an airborne three-line sensor camera for taking pictures of a selectedpiece of land in three directions, that is, forward obliquely,vertically and backward obliquely; a gyro mounted in the housing of thethree-line sensor camera for determining the attitude of the camerawhile photographing; a GPS for providing the instantaneous position dataof said camera in the three-dimensional space; a stabilizer forcontrolling the attitude of said camera to set its optical axis to bevertical at all times, and at the same time for absorbing vibrations ofthe aeroplane; a data processing unit for processing attitude data fromsaid gyro and position data from said GPS and outputting signals forcontrolling said stabilizer; a data recorder for recording the landimage data from said camera, the attitude data from said gyro and theposition data from said GPS; an image display for showing the land imagedata from said camera; and a data analyzer for converting the land imagedata from said camera into the land image data given in terms of fixedcoordinates on the basis of the land image data, attitude data andposition data all recorded by said data recorder, and for outputting theso converted land image data.